Journal of clinical monitoring and computing
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J Clin Monit Comput · Jan 2000
ReviewAtelectasis formation during anesthesia: causes and measures to prevent it.
Pulmonary gas exchange is regularly impaired during general anaesthesia with mechanical ventilation. This results in decreased oxygenation of blood. A major cause is collapse of lung tissue (atelectasis), which can be demonstrated by computed tomography but not by conventional chest x-ray. ⋯ In summary, atelectasis is present in most humans during anaesthesia and is a major cause of impaired oxygenation. Avoiding high fractions of oxygen in inspired gas during induction and maintenance of anaesthesia may prevent formation of atelectasis. Finally, intermittent "vital capacity"-manoeuvres together with PEEP reduces the amount of atelectasis and pulmonary shunt.
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Improving the prediction of successful ventilator weaning and extubation is a goal that all Intensivists and perioperative physicians strive for. The successful wean and extubation of ventilated patients decreases hospital length of stay and associated costs, but more importantly it also reduces patient morbidity and mortality. ⋯ We also review the non-respiratory factors affecting weaning and the role of the bedside nurse and respiratory therapist. Resolution of the pulmonary compromise and an understanding of respiratory physiology, used in conjunction with monitored indices of weaning parameters in a consistent fashion will continue to improve our success rates of ventilator weaning and extubation.
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Traditionally, the study of CO2 and O2 kinetics in the body has been mostly confined to equilibrium conditions. However, the peri-anesthesia period and the critical care arena often involve conditions of non-steady state. ⋯ The lesser known area of non-steady state O2 kinetics is introduced, including the measurement of pulmonary O2 uptake per breath. Future directions include the study of the respiratory quotient per breath, where the anaerobic threshold during anesthesia is identified by increasing respiratory quotient.
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J Clin Monit Comput · Jan 2000
ReviewHRCT imaging of airway responsiveness: effects of anesthetics.
The noninvasive imaging method, high resolution computed tomography (HRCT), has been developed in animal models and applied to humans with obstructive lung disease for assessing regional and individual airway responsiveness. The ability to directly view airway responses during provocations such as tracheal intubation in an asthmatic could greatly enhance our understanding and treatment of airway hyperresponsiveness. HRCT uses increased kilovoltage peak (kVp) and milliamperage (mAs) settings, thin slices, high spacial frequency reconstruction algorithms, and small fields of view to resolve structures as small as 200 microm. ⋯ HRCT allows direct in vivo measurement of airway responsiveness to pharmacological and physiological stress that induces bronchoconstriction or bronchodilation. Using HRCT, we are able to measure airway dilation at baseline airway tone with inhalation anesthetics, differentiate the bronchodilating properties of inhalational agents in airways with tone, assess bronchodilating agents commonly used as premedications prior to anesthesia, and measure airway heterogeneity at baseline tone and their response to a variety of stimuli. This ability of HRCT to measure airway caliber and response heterogeneity in vivo noninvasively will dramatically improve our understanding of pulmonary physiology in general and the effects of anesthetics on the airways specifically.
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J Clin Monit Comput · Jan 2000
ReviewEffects of high thoracic epidural anesthesia and local anesthetics on bronchial hyperreactivity.
Bronchial hyperreactivity can cause life threatening bronchospasm after airway irritation. Therefore, endotracheal intubation is avoided in asthmatics when feasible. High thoracic epidural anesthesia can be used to avoid endotracheal intubation and offers less postoperative pulmonary complications when compared to systemic postoperative analgesia. ⋯ The attenuation of bronchial hyperreactivity can be shown as a dose dependent effect of lidocaine and bupivacaine. The intravenous effect of lidocaine is comparable to the effect of a moderate dose of salbutamol and leads to an additive effect when both drugs are used in combination. Overall, high thoracic epidural anesthesia can be used safely in patients with bronchial hyperreactivity and intravenous administration of lidocaine (1.5-2.0 mg x kg(-1)) can be used as a prophylactic treatment prior to airway instrumentation.